The invention relates to an electric warning device according to the preamble of claim 1, a brake lining module equipped therewith and a disk brake equipped with such a brake lining module.
An electric warning device having the features of the preamble of claim 1 is known from German patent 33 07 394 (DE 33 07 394 C2). The electric warning device for indicating worn friction linings substantially comprises a plug with a head and a shank, which has a longitudinal groove for receiving an electric conductor. The electric conductor is usually inserted as a U-shaped loop into the longitudinal groove of the plug and fastened by means of the plug to the brake lining. To the end, the brake lining in the friction lining material has a mostly radially extending bore, into which the plug is inserted and fixed in position by a clamping or spreading action or alternatively by sealing with an adhesive (synthetic resin or the like).
The electric conductor itself is generally a litz wire with an insulating wrapper. The conductor is connected to an electric circuit which closes when, as a result of advanced friction lining wear, the brake disk has ground through the plug and the insulating wrapper of the conductor and is touching the conductor. When the conductor is fashioned in the shape of a loop, it may form a constituent part of a so-called break circuit which is interrupted when, as friction lining wear progresses further, the conductor is fully severed.
In the brake lining module known from DE 33 07 394 C2 the electric conductor, before it reaches the head of the plug, is passed through a tubular rivet which is used to support a brake lining hold-down spring pivotally on a projection of the back plate of the brake lining. The hold-down spring is supported on the bridge of a floating caliper of a floating-caliper disk brake. The arrangement prevents the electric conductor from becoming nipped between the hold-down spring and the back plate of the brake lining. However, such a style of construction calls for a radial gap of approximately 10 mm between the radially outer edge of the brake lining and the vehicle wheel rim, with which the brake cooperates.
In heavy-duty disk brakes the brake disk is to have as large a diameter as possible in order to be able to achieve a sufficiently high braking torque for fast and heavy vehicles and hence also reduce the load per unit area of the so-called brake disk path and at the same time obtain a larger heat-dissipating surface. The brake disk path is the annular surface where, during braking, the friction linings are supported against the brake disk. Frequently the brake disk diameter is to be increased without increasing the diameter of the wheel rim. This may be achieved only by utilizing the clearance between the wheel rim and the brake disk as far as is constructionally possible. The smaller the clearance still remaining between the wheel rim and the brake disk is, the greater the risk of damage to the electric conductor, e.g. as a result of its being nipped between two components.
The object of the invention is to provide an electric warning device for indicating excessive friction lining wear and a brake lining module equipped therewith, which takes up less radial installation space than was previously customary and yet reliably prevents damage to the electric conductor. In particular, nipping of the electric conductor between the back plate of the brake lining and a hold-down spring is to be avoided.
The object is achieved according to the invention by an electric warning device having the features indicated in claim 1. Accordingly, the extension provided on the plug extends from the protective shield over the joint centre plane of the plug shank and of the longitudinal groove, in which the conductor is accommodated, up to, say, at least the opposite plug shank edge so that the electric conductor is forced by the extension into a direction deflected through approximately 90 degrees. According to the invention, therefore, the electric conductor of the electric warning device is led away in a manner that takes up only a small amount of radial installation space and is moreover well protected. The plug fastening the electric conductor in the friction lining may be provided radially at the inside or radially at the outside of the brake lining.
In accordance with an advantageous development of the electric warning device according to the invention, the extension extends not only up to, say, at least the opposite plug shank edge but even beyond the edge of the head of the plug shank. By the means, even more reliable guidance of the electric conductor in the desired direction is achieved.
In many embodiments of the electric warning device according to the invention, the extension extending from the protective shield is of a resiliently compliant design such that it may exert a force acting in the direction of the plug shank upon the electric conductor. The effect thereby achieved is that the conductor in the region of the warning device is led away in as flat a manner as possible even when the conductor at its further extension is acted upon by forces attempting to pull it in another direction. In other embodiments, the extension is rigid and stable enough to retain its preset orientation to an adequate extent even when forces act upon it.
The invention also relates to a brake lining module which is equipped with an electric warning device of the previously described type. In the brake lining module according to the invention, the back plate of the brake lining in a radially situated, friction-lining-free region is provided with a recess, which is open towards the radial edge of the back plate and through which the electric conductor is passed. The extension of the warning device according to the invention forces the conductor into the recess of the back plate. The recess of the brake lining back plate and the bore in the friction lining material, in which the plug of the warning device is fastened, have centre planes which are mutually adjacent in order that the conductor may be led as quickly as possible out of the most temperature-stressed region close to the brake disk. Preferably, the recess of the brake lining back plate and the bore in the friction lining material have a common centre plane.
In embodiments of the brake lining module according to the invention with a resilient extension, the latter exerts a force pressing the electric conductor back into the recess if for some reason the electric conductor has a tendency to leave the recess of the back plate.
In accordance with an advantageous development of the brake lining module according to the invention, the extension of the warning device extends as far as into the recess of the back plate. The electric conductor is therefore held even more reliably in the recess of the back plate and the risk of pinching of the conductor between the edge of the brake lining back plate and a hold-down spring is further reduced.
The present invention also relates to a disk brake, in particular a vehicle disk brake, which is equipped with a brake lining module according to the invention. Such a disk brake, for example a floating-frame disk brake, may utilize the clearance between it and a wheel rim to the maximum extent.
In a preferred embodiment of the disk brake, a spring arm of a hold-down spring acting upon the brake lining module closes the radially open edge of the recess of the brake lining back plate, through which the electric conductor is guided. In the manner the electric warning device with its conductor is still held in the friction lining even if the adhesive, which is supposed to secure the plug in the bore of the friction lining, has decomposed for example as a result of excessive heat.